Fin forming roll



Feb. 23, 1954 w. P. HILL 2,669,893

FIN FORMING ROLL Original Filed Sept. 25, 1950 5 Sheets-Sheet l f\. a Iy 2:5? 2. 4/44 47% yflzmw Feb. 2-3, 1954 w, I fl 2,669,893

FIN FORMING ROLL Original Filed Sept. 25, 1950 3 Sheets Sh t 2 INVENTOR.

69174-7? M14 BY Feb. 23, 1954 w. P; HILL FIN FORMING ROLL 3,Sheets-Sheet 3 Original Filed Sept. 25, 1950 g E ORA/5 7-5 M ytwrae A rr46 l ea Patented Feb. 23, 1954 FIN FORMING ROLL Walter P. Hill, Pontiac,Mich., assignor to Gain met & Hecla, Inc., a corporation of MichiganOriginal application September No. 186,597. Divided and this 25, 1950,Serial application January 29, 1951, SerialNo. 208,301

6 Claims. 1

This invention relates to an improved roll for use in the manufacture ofintegral finned tubing and is a division of my copending application,Serial No. 186,597, filed September 25, 1950, now Patent No. 2,610,452.

Rolls of the general type forming the subject matter of this inventionare shown in the Walter P. Hill Patent No. 2,508,518, dated May 23,1950; and are highly satisfactory for use in the production of tubinghaving an integral helically extending fin of substantial heightprojecting outwardly from the peripheral surface of the tubing. In themanufacture of such finned tubing, three forming rolls are usuallyemployed, and these rolls are rotatably supported with their axes spacedfrom each other equal distances around a length of tubing. The axes ofthe rolls are inclined with respect to the axis of the length of tubingat an angle corresponding to the mean helix angle of the fin to beformed on the length of tubing, and the rolls are driven in trackingrelationship about their respective axes.

In operation, the rolls or peripheral edges of the discs apply aradially inwardly directed pressure on axially spaced helically alignedportions of the outer surface of the length of tubing, causing materialfrom the outer surface of the tubing to flow or extrude outwardly intothe annulargrooves between adjacent discs. In cases where the helixangle of the fin is very small in order to obtain a large number of finconvolutlons per unit of length of the tubing, and where the outsidediameter of the fin is large in comparison to the root diameter of thefin, difficulty is encountered in passing the peripheral portions of thediscs through the helicoidal path provided between adjacent convolutionsof the fin being formed without displacing the fin convolutions axiallyof the tube. Such interference causes the fin convolutions to move backand forth along the tube axis during the forming or rolling operationand not only unduly wears the roll discs, but in addition, work hardensthe material to such an extent that any attempt to raise a high fin fromthe tube fractures either or both the fin and tube. The above objectionmay be overcome by contouring the side surfaces of revolution of theindividual discs, so that the peripheral portions of the latter willpass relatively freely through the helicoidal path between adjacentconvolutions of the fin during the forming operation.

In the Walter P. Hill Patent No. 2,508,518 the opposite side surfaces ofrevolution of the discs converge toward the outer edges of the discs andare convex in contour radially of the discs. This contour provides therelief required for the pe ripheral portions of the discs to passrelatively freely through the helicoidal path between adjacentconvolutions of the fin, and thereby avoid the interference noted above.

Although forming rolls composed of contoured fin forming discs of theabove type render it possible to produce integral high finned tubing ona production basis, difficulty has been encountered in forming the rollswith the accuracy required for optimum results. Owing to the fact thatin such forming rolls the annular space existing between adjacent discsis very small, it is not feasible to provide a grinding wheel thinenough to operate within this space. Accordingly, it is not prac ticalto form grind the discs while assembled in roll formation, and it hasbeen the practice to individually form grind the discs prior toassembling the same. More particularly, the contoured work performingside surfaces of the discs were form-ground with reference to one ofboth flat ends of the hub portions of the discs, and subsequent to thegrinding operation, the discs were grouped in assembled relationship toform the roll.

It follows from the above that allowable manufacturing errors ingrinding the individual discs,

I although small, nevertheless become accumulativc when the discs aresecured in assembled relationship; and in some cases, the accumulativeerror which may be different for each roll of the series, is sufiicientto cause the interference discussed above between the discs and finconvolutions during the rolling operation.

With the above in view, it is an object of this invention to simplifyand reduce the cost of forming the roll discs as well as eliminate theaccumulative error referred to in the preceding paragraph. This isaccomplished according to the present invention by forming or contouringthe peripheral portions of a group of roll discs while the latter aresupported in substantial spaced relationship in the same order theylater assume when assembled to provide a forming roll. Moreparticularly, a plurality of disc blanks corresponding in number to thenumber of preformed discs of a roll are supported on an arbor withadjacent discs spaced axially from one another a distance suflicient toaccommodate a forming tool such as a grinding wheel. The tool and arborare relatively moved in directions to engage the tool with oppositesides of successive blanks. A preformed template is provided forcontrolling the path of relative movement of the tool and arbor so thatthe peripheral portions of the aeeasee blanks are successively fashionedto the specified contour of the finished roll discs regardless ofvariations in thickness of the discs. The finished discs are thenremoved from the arbor and are secured together in juxtaposition in thesame sequence they assumed during the forming operation. By followingthis procedure in forming each set of rolls employed to extrude ahelical fin from a length of tubing, bending of the convolutions of thefin during the forming operation by reason of inaccuracies in themanufacture of the roll discs is reduced to a minimum. Also a superiorfinned tube is produced with less wear on the discs and maintenancecosts are accordingly reduced.

It is a further object of this invention to provide an arrangementwhereby one or more discs may be replaced in the group of discs formingthe roll without destroying the accuracy of the roll. In

accordance with this invention, when it is desired to replace a disc,all of the usable original discs are again assembled on the tool arborin the same relationship they assumed during the original formingoperation, and the replacement disc blank is installed on th arbor inthe position previously occupied by the disc it replaces. Thus all ofthe discs are subjected to the finishing operation, so that thereplacement disc or discs will have the same relationship to theremaining discs as the original discs.

The foregoing as well as other objects will be made more apparent a thisdescription proceeds, especially when considered in connection with theaccompanying drawings, wherein;

Figure 1 is a semi-diagrammatic plan View of apparatus embodying thefeatures of this invention;

Figure 2 is a sectional view taken on the line 2--2 of Figure 1;

Figures 3, 4 and 5 are respectively sectional views taken on the lines3-3, 4-4 and 5-5 of Figure 1;

Figure 6 is a sectional 66 of Figure 1;

Figure '7 view through a ed in accordance view taken on the line part ofa forming roll constructwith this invention;

Figure 8 is an enlarged side elevational view, partly in section, ofapart of the apparatus shown in Figure l; I

Figure 9 is a sectional view taken on the line 9--9 of Figure 8;

Figures 10 and 11 are semi-diagrammatic views considerably enlarged toillustrate certain features of the apparatus shown in Figure l.

The method and apparatus to be presently described in detail isparticularly suitable for manufacturing forming rolls of the type shownin Figure '7 of the drawings and designated by the numeral $2. Thisforming roll comprises a drive shaft l3 and a plurality of discs M. Thediscs are centrally apertured to receive the drive shaft 13, and arekeyed or otherwise secured to the drive shaft for rotation by'thelatter. The discs i4 have central hub portions l5 of uniform axialdimension and have peripheral portions It. The opposite side surfaces llof revolution of the peripheral portions it converge from the hubportions i5 to the outer edge of th discs l4.

The discs it as assembled on the shaft 13 with the hub portions If: incontact and adjacent peripheral portions !6 cooperate with oneanother toprovide annular grooves 18 therebetween. The number of discs i l securedto the shaft. 13 may vary to suit different conditions, but for thepuris an enlarged longitudinal sectional d pose of illustration, sevendiscs are shown. These discs are individually identified in Figure 7 ofthe drawings by the reference numerals is to 25 inclusive.

As disclosed in the Walter P. Hill Patent No. 2,598,518, a set of threerolls ii! are suitably supported around a length of stock or tubing, andcooperate with one another to extrude material from the outer surface ofthe stock to form a helically extending fin of substantial height on thestock. The rolls are supported with their axes crossing the axis of thestock at an angle depending uponthe helix angle of the fin to be formedon the stock and this angle is usually small in order to provide a largenumber of fin convolutions per unit of length of the stock. The discs Mon the respective rolls are in tracking relationship and the peripheraledges of at least the discs at the front ends of the rolls apply apressure in a radially inward direction on axially spaced helicallyaligned portions of the outer surface of the stock. An opposite orradially outward force results from the application of said radiallyinward force on the stock and this outward force displaces or extrudesmaterial from the surface portion of the stock outwardly between theaxially spaced portions or into the annular grooves l8 formed by theperipheral portions of the discs.

With the above in view, attention is again called to Figure 7 of thedrawings, wherein it will be seen that the first four discs is, 2c, 2!and 22 are the pressure applying or working discs; and the last threediscs 23, 2d and 25 are more or less the fini hing discs. The workingdiscs iii to 22 preferably progressively increase in diameter from thefirst disc l9 to the last disc 22 of this group in order toprogressively displac material from the outer surface of the stock andat the same time, materially reduce the unit load on'any one disc. Thefinishing discs 23, 24 and 25 may be practically the same diameter asthe final working disc 22 since the principal function of the finishingdiscs is merely to guide or straighten the fin convolutions formed bythe working discs.

The peripheral portions N3 of the discs 14 progressively increase inthickness from the first working disc IE! to the final working disc 22with the result that the grooves 18 between the working discsprogressively decrease in width from the first groove to the lastgroove. The purpose of this construction is to enable the side surfacesll of revolution to guide the material as it is extruded into arelatively thin high fin.

The helical fin produced with forming rolls of the above general typehave adjacent convolutions closely spaced and of substantial height incomparison to the root diameter of the fin. The diameter of the discs Itis necessarily substantially larger than the outside diameter of thefin; and in practice, the rate of withdrawal of the discs from thespaces between adjacent convolutions of the fin is somewhat differentthan the rate of axial movement of the stock during the fin formingoperation. This being the case, the peripheral portions it of the discs14 interfere with the convolutions of the fin, and the lat.- ter areactually bent backwardly and forwardly during the fin forming operation.This is objectionable in that some work hardening of the materialresults, and considerable stress is applied to the peripheral portionsof the discs. In order to overcome the above objection, the sidesurfaces of revolution of at least the working discs 19 to 22. inclusiveare contoured inorder to pass relatively freely through the helicoidalpath provided between adjacent convolutions of the fin being formed bythe roll. In detail the surfaces of revolution I! on the working discs|9 to 22 inclusive are convex and curve radially with respect to theaxis of the roll. This general elliptical curvature affords ampleclearance to enable Withdrawal of the discs from the spaces betweenadjacent convolutions of the fin without appreciably bending orstressing the fin.

If desired the side surfaces of revolution of the sizing or finishingdiscs 23 to 25 inclusive may correspond in contour to the side surfacesof revolution of the working discs I 9 to 22 inclusive. However, in thepresent instance, the opposite side surfaces of revolution of the sizingdiscs 23 to 2-5 inclusive are straight in radial contour as clearlyindicated in Figure 7 of the drawings. Such a construction has theeffect of work hardening the convolutions of the fins after they havebeen formed by the working discs, and in some instances, this result isdesired. Inasmuch as the work hardening takes place after the fin hasbeen formed, it does not interfere with extruding the material to form ahigh fin.

In the manufacture of forming rolls of the above type, it has been foundthat when the discs M are individually machined 01' formground to thespecified contour without regard to their ultimate assembledrelationship, any error, no matter how slight, in the grinding of singlediscs becomes accumulative when the discs 4 are subsequently securedtogether to form a roll. .Although the allowable tolerances in formingindividual discs may be small, nevertheless, the accumulative error,over the group of discs may be sufficient to cause the discs'to deformthe fin during the fin forming operation. As a result such accumulativeerrors frequently promote work hardening of the metal during forming ofthe fin and cause excessive wear of the forming discs.

The foregoing is overcome in accordance with the present invention byproviding a method and apparatus for manufacturing the discscharacterized in that the peripheral portions I6 of all of the. discs I4 are fashioned or form-ground while the discs are supported in the samerelationship they subsequently assume when assembled to provide theforming roll |2. Also,

as will be more fully hereinafter described, the roll discs M arefashioned so that when they are assembled the median planes P of the hubportions |5 of adjacent discs I 4 are spaced equal distances from oneanother regardless of any variation in thickness of the peripheralportions Hi of the individual discs. The planes P shown in Figure 7 ofthe drawings are perpendicular to the roll axis and pass through theaxial centers of the tips of the discs l4. Thus, the grooves l8 areaccurately located with respect to each other axially of the roll sothat little or no axial stress is applied to the material being extrudedinto the grooves I9. Also, when a plurality of rolls l2 are distributedabout a length of tubing, the grooves lsaccurately track and the desiredhelically extending fin is produced with a minimum amount of resistance.v

The various steps of the method of manufacture will be more readilyunderstood upon considering one specific form of apparatus capable ofcarrying out the steps of the method. With this in view, reference ismade more in detail to Figure 1 of the drawings, wherein the numeraldesignates a pantograph form grinder having ill a work holding assembly3| and having a forming tool assembly 32. The work holding assembly 3|comprises a base 33 and a compound slide 33 suitably supported on thebase. The compound slide 33' has two slides 34 and 34. The slide 34 isadjustable relative to the base 33 in a longitudinal direction and theslide 34' is adjustable relative to the slide 34 in a directionextending transverse to the direction of movement of the slide 34.Suitable hand operated controls 35 and 35" are respectively connected tothe slides 34 and 34 in a manner shown in Figures 2 and 6 of thedrawings for independently adjusting the slides. I

A spindle 35 is journalled in a bearing 36 suite ably secured to theslide 34 in a manner such that the axis of the spindle extends in thedirection of movement of the slide 34. The front end of the spindle 35is coupled to the drive shaft of an electric motor 37, and a suitablebracket 38 is provided for securing the motor on the slide 34. The rearend of the spindle is provided with a center 38', which cooperates witha center 31 to support an arbor 39. The center 31 is mounted on abracket in axial alignment with the center 39, and the bracket 40 issuitably secured to the slide 34. The bracket 40 has a bearing part 40within which the center 37 is supported for sliding movement in thedirection of its axis and a suitable hand operated control 4| isprovided for sliding the center 31. The arrange: ment is such as topermit the arbor 39 to be readily inserted between and removed from thecenters. The arbor 39 is rotated as a unit with the spindle 35 by meansof a pin or lug 4| extending from the rear end of the spindle in aposition to engage a fiat 42 (Figure 8) on the adjacent end of the arbor39.

The arbor 39 is shown in Figure 8 of the drawings as having acylindrical part 44 projecting rearwardly from the head 43. The frontside of the head 43 is fashioned with a recess at the center forreceiving the center 38 on the rear end of the spindle 35, and the rearend of the part 44 has a reduced threaded portion 45 which also has arecess at the end thereof for receiving the center 31'. The purpose ofthe arbor 39 is to support a plurality of disc blanks 46 in operativerelation to the forming tool 32. The disc blanks 46 are centrallyapertured and are sleeved on the part 44. The first or forwardmost blankis seated against a stop in the form of an annular bearing surface 4! onthe head 43 of the arbor, and spacer rings 48 are supported on the part44 of the arbor between adjacent blanks in order to provide sufficientclearance between the blanks for the grinding disc 52. All of the discblanks 46, together with the spacers 48, are clamped in assembledrelationship against the head 43 by a cap 49 sleeved upon the rear endof the part 44 in a. position to engage the rear side of the last discblank and held in place by a nut 50 threaded on the portion 45 of thepart 44.

The number of disc blanks 46 on the arbor 39 corresponds to the numberof preformed discs |4 employed to form the roll it, and in the pres,-ent instance seven disc blanks are shown. These disc blanks areindividually indicated in Figure 8 of the drawings by the referencenumerals l9 to 25 inclusive, and these blanks respectively correspond tothe preformed discs is to 25 inclusive. The disc blanks 4%; are rotatedas a unit with the arbor 39; and for accomplishing this result, thecylindrical part 44 is provided. with meanes- 7 a. longitudinallyextending: keywhich. extends into registering: key slots formed in the:respective disc blanks.

The forming tool. assembly 32 comprises. a grinding wheel disc: 52secured to the front; end of a. spindle 53, and rotatable. by thespindlevv in a; plane. normal to the. axis: of the arbor 39. Thegrinding wheel disc: 52 is. relatively thin, and is located by thespindle in a position. opposite the arbor 39; The spindle 53 driven: by"an electric motor 54. which in turn is supported on a slide 55. Theslide. 55 is supported for move.- ment; in opposite directions normalto: the axis of the arbor in order to permit movement: of the grindingwheel disc 52 in directions: toward and away-from the arbor axis.

As shown particularly in Figure 5 of. the.draw ings, theslide 55 ismounted on a second slide 55 supported on the frame of the machine. for

movement in opposite directions parallel to the axis of the arbor 39'.Thus the: grinding wheel disc" 52, in addition to being movable towardand away from the axis of the arbor 39, is also capable of being movedalong the axis of the arbor; Such movement of the grinding wheel 52relative to thearbor enables engaging the grinding wheel with oppositesides of the peripheral" portions of successive disc blanks 26 on thearbor;

In accordance with path of movement of the: present invention, the thegrinding wheel discs 52 relative to the arbor 39 is controlled by amaster cam or template 51. As shown particularly in Figures 1 and 3 ofthe drawings, the master template 5? s-iti'oned' on the machine frame bypins and removably secured to the frame by suitable fastener elements59. The template 5?: is spaced some distance from the arbor 39 andextends in the same direction as the axis of thearbor.

The inner edge of the template 51 is provided with a series of lateralprojections 60 which are spaced from each other in the direction oflength of the template and correspond in number to the number ofpreformed discs l4- employed to formthe roll l2. In the present instanceseven projections are provided on the cam, and these projections areindividually identified by the numerals [9'' to 25 inclusive. Theprojections l5 to25' respectively correspond to the perlpheral portions16 of the preformed discs 19 to 25 inclusive, and the edges or theprofile of the projections are accurately formed to correspond exactlyto the contour of the peripheral portions of the respective discs 14.The size of the projections 60, however, is preferably many timesgreater than the size of the peripheral portions l6 of the discs I4 inorder to facilitate manufacture. For the purpose of this illustration,the actual size of the projections 50 on the cam or template 5! is sixtimes the size of the peripheral portions of the discs Id. Also in theinterests of convenience in manufacture, the space between adjacentprojections 60 isa multiple of the space between adjacent disc blanksl8; and in the present instance, the space between adjacent projections60 is six times greater than the space between adjacent disc blanks 46.The master cam or template 5! is engaged by a follower 6| in the form ofa pin, and the pin is in turn connected to the grinding wheel disc 52 bya pantograph arrangement of linkage designated generally by thereference numeral 62. The pantograph arrangement of linkage 62 connects:the master cam or template 51 to the comprises a flat strip pogrinding;disc; 52: with. a ratio of: six to.- onc. In other words: the grinding:whceli disc: is; moved throughout the. path dictated: by the. master.template at a rate whichis /5 therate of movement of the; follower 61along the template. with. the result. that. the. grinding wheel disc.successively engages opposite sides of. the peripheral portionsoftheblankstii onthe arbor 39...

In. detail the follower 61. is: supported; on. the. lower end. of alink. 83. and. the upper. end. of the link. 5 is pivoted. by av pin: 64to: the. upper end; of'alink 65.. The link 65 is; the same.- length as;the link 6:3,. and is pivoted at its lower. end to. a. bracket 66;rigidly fixed on. the machine frame. The link 63 is. connected to theslide by a link. 68. positioned at. the. inner: side. of the link inparallel. relation to. the. latter and. having one end. pivoted to the.link. 15.2 by a. pin 69;. The other. end of the. link 68. is pivoted bya pin. ill. to the slide. 55 and to; the inner end of a short. link H:having the. outer end pivoted. by a pin. 12 to the. linkx55. The.distance. between the axes of. the. pins 111" and. 12 is equal to. thedistance. between the. axes. of the pins 54 and to. Also, the; distancebetween the pivot pins 6'4 and 12'. is: the same. as. the. distancebetween the. pins 69: and 1.0, with the result that aparallelogram. is.formed- In. addition it: will be. noted. that. the distance. between:the pivot pins M and 6.9: is equal to. one sixth the. length 0! the.link; 63. As a consequence, movement of' the follower B5 in and: out.relative. to. the. master cam 57! moves the grinding. wheel 52 or slide55 through the medium of the parallelogram linkage previously describedin. corresponding directions at a. rate one sixth the. rate of movementof the follower El. Likewise any displacement of the follower tit backand. forth along: the master cam 51 causes thev parallelogram linkage toapply a side thrust on the slide. 55 which. is transmitted. to: theslide. 55. Thus the slide 55 moves the grinding wheel 52 or slide. 551back and forth. along the arbor 39 at a. rate one sixth the. rate. ofmovement. of the follower 61' T5131. tive to the cam 51.

The numeral '35; in Figure l of the drawings designates a dressingdevice for the periphery of the grinding wheel. 52'. Briefly, the.dressin devicev 15 is supported on. the machine frameat the. side of thegrinding wheel spindle- 53 opposite the. side occupied by the arbor 39..The device 15. comprises a slide '15 and a. dressing. tool 1?. Theslideit issnpported on themachlne frame for movement: toward and away fromthe grinding wheel spindle 53'; and the tool 11 is supported forrotation in a plane normal to the plane of rotation of the grindingwheel 52. The slide 16 is movable toward and away from the periphery ofthe grinding wheel 52 by a hand wheel 18 mounted on the outer side ofthe machine frame in a position where it may be conveniently:manipulated by the operator.

The dressing tool 1''! is positioned to require movement of the grindingwheel 52 forwardly and outwardly from its normal operating posi tionrelative to the arbor 39 in order to bring the periphery of the wheel 52in operative relation to the tool 11. Movement of the wheel 52 to itsdressing position is facilitated by providing a hole 19 in the machineframe for engagement with the follower pin 61'. In this connection itwill be noted that the pin 5| is slidably supported on the outer end ofthe link 63 to permit dropping the same into the hole 19. The

.ly illustrated herein as this hole 19, the grinding wheel 52 is movedfrom its normal position shown by the full lines in Figure 1 to thedressing position shown by the broken lines in the same figure. Afterthe grinding wheel '52 is located in its dressing position, the handwheel 73 is manipulated to bring the point of the tool It intoengagement the wheel 52. The dressing device and the means for operatingthe same is merely diagrammaticalinvention is not concerned with thedetails of construction of the same.

Operation The first step in the operation after an arbor 39 with a setof disc blanks 46 is supported on the centers 3? and 38', is to rest thefollower 6| on the extreme inner edge of the first master cam projectionIt". This movement of the follower BI through the linkage 62 shifts thegrinding Wheel 52 rearwardly and inwardly relative to the arbor 39 tolocate the periphery of the wheel 52 in registration with the first discblank I9 on the arbor 39. The compound slide of the work holder assembly3! is then adjusted relative to the grinding wheel disc 52 to bring theperiphery of the wheel 52 into grindng contact with the periphery of thefirst disc blank I9 and the first disc I9 is ground to the desireddiameter.

Upon completion of the above operation, the follower fiI is shifted tothe broken line position shown in Figure 1 and the work holder 3| isagain adjusted until the front side of the wheel 52 sparks against therear side of the first disc I9. The arbor 39 and grinding wheel 52 arethen in their proper relative positions and the follower BI is manuallymoved successively along the profiles of the cam projections Is" to 25".Owing to the pantograph linkage connection 62 between the follower 6|wheel 52, the latter successively engages opposite sides of the discblanks 45 and forms the peripheral portions of the blanks to the exactprofile contour of the cam projections 60. This operation is illustratedin the exaggerated views (Figures 10 and 11 of the drawings) andattention is called to the fact that the disc blanks 46 and camprojections 60 are axially spaced relative to each other so that theplanes P between the opposite side surfaces of the hub portions I 5 ofadjacent discs I4 of the roll I2 are predeterminedly spaced, or in thepresent instance, are spaced equal distances from one another regardlessof any variations that may exist of the discs I 4. As a result when therolls I2 length of tubing the grooves 58 are arranged in accuratetracking relationship and material is extruded from the tubing by theroll discs I4 with a minimum amount of resistance.

It will be apparent from the above that the peripheral portion or eachdisc blank on the arbor is ground to the exact contour of itscorresponding cam projection on the master cam 57. The profile contourof the cams $9" to 25" in turn respectively corresponds to thepredetermined contour of the roll discs I9 to 25 so that upon completionof the grinding operation on the blanks I9 to 25 inclusive, one completeset of and the grinding roll discs I 4 is provided. Thesediscs are thenremoved from the arbor 39, and are assembled as'shown in Figure 7 of thedrawings on the shaft I3 in the same sequence they previously occupiedwhen a plurality of rolls I2 formed in the above manner are groupedaround a length of stock to be finned, the spacing surfaces ofrevolution of the rolls in the group is individual discs.

Also with the above method and apparatus one or more of the preformeddiscs I4 may be replaced without destroying the accuracy of therelationship described in the preceding paragraph. Assuming for thepurpose of illustration that it is desired to replace the forming disc22 of the roll I2, all of the discs 54 are removed from the shaft I3 andwith the exception of the disc 22 are assembled in the same sequence onthe arbor 39. A disc blank 22' is substituted for the preformed disc 22and the grinding operation described above is repeated. During thisgrinding operation the blank 22' is fashioned to the contour of the disc22 and the amount of stock removed from the discs I9, 20, 2|, 2%, 24 and25 is sufficient only to insure obtaining the desired relationshipbetween the discs when they are again assembled on the roll shaft I3.

What I claim as my invention:

1. A fin forming roll comprising a plurality of individual discs, eachdisc provided with a central hub portion and with a surrounding portionhaving the opposite side surfaces converging toward the periphery of thedisc, said discs being secured together in axial alignment with the hubportions of adjacent discs in contact and with the side surfaces ofadjacent discs spaced axially from each other to form annular spacestherebetween, the surrounding portions of the discs progressivelyincreasing in thickness to provide the annular spaces between adjacentdiscs with progressively decreasing widths and the median planes betweenthe side surfaces of adjacent discs being spaced equal distances fromone another.

2 The fin forming roll defined in claim 1 in which the side surfaces ofeach disc are convex on a curve which extends radially outwardly fromthe hub portion of the disc to the outer edge of said disc.

3. A fin forming roll comprising a series of discs secured in coaxialrelationship with the central portions of the discs in side by siderelation, said discs having fin forming portions surrounding the centralportions and having the opposite side surfaces of the fin formingportions converging from the central portions of the discs to the tipsat the periphery of the discs, said fin forming portions progressivelyincreasing in width from the first disc to the last disc in said seriesto provide annular spaces between adjacent discs which F progressivelydecrease in width from the first annular space to the last annularspace, the median planes of the central portions of the discs extendperpendicular to the axis of the roll and respectively pass through thetips at the periphery of the discs midway between opposite sides of thetips, and the median planes of adjacent discs being spaced equaldistances from one another axially of the roll.

4. The fin forming roll defined in claim 3 wherein the central portionsof the discs are of uniform width and wherein the central portionsprising a second series of discs 11 are secured together with adjacentsurfaces :in abutting relationship.

"5. The fin forming r011 defined in claim 3 wherein the oppcsite'sidesurfaces of-the-fin ferming portions are ccnvexedly curved throughoutsubstantially the full radial extent of said surfaces.

6. The fin forming roll defined in claim 5 comhaving central "portionscoaxially arranged with respect to the central portions of the firstseries of discs :and. having finishing portions surrounding 'thecentralportions, the finishing portions having the :opposite side surfacesrespectively lying in planes which converge from'the central portions,of the discs to the tips of the latter to provide annular nn receiving:grocves median-planes OflthB discsintheesecondzseriesrex tendperpendicular between 1 adjacent adiscs, *Lthe to the 11011 axis -and:pass through the tips midway between opposite fid68 the same as thedistance between the :median planes of adjacent discs in the firstseries.

'WALTER LP.

References Cited .in the file 10f this patent "UNITED STATES PATENTSNumber Name Date 1,909,005 Paugh May 16, "1933 2,429391 Schuler Oct.'21, I947

